The present invention relates generally to fastener-driving tools, and more specifically to such tools operating under pneumatic power, also referred to as nailers.
In conventional pneumatic nailers, such as those disclosed in U.S. Pat. No. 3,638,532 and US Patent Publication No. 2012/0223120 incorporated by reference, the nailer is pressed down upon a workpiece needing a fastener, and in so doing, a workpiece contact element (WCE) is retracted relative to the tool housing. User depression of a trigger activates a trigger valve, which directs pneumatic pressure within the tool such that a piston is driven down a cylinder to impact and drive a fastener into the workpiece.
In the course of driving the piston down the cylinder, the pneumatic pressure is diverted to a return chamber within the tool housing. Once the fastener is driven, the user typically releases the trigger, and/or lifts the tool from the workpiece, which allows the WCE to return to its start position. When either of these conditions occurs, the trigger valve closes and pressure in the return chamber pushes the piston hack to the start position. As the trigger is released, the main system pressure closes the main valve on top of the cylinder to prepare for the next cycle.
In pneumatic nailers, traditionally, the piston was provided with a resilient annular seal, similar to an “O”-ring. However, after prolonged use, friction between the seal and the cylinder caused wear on the seal, which as tool use continued, allowed blowby in the cylinder, or the passage of some pressurized air past the piston, reducing tool power.
A proposed solution to the blowby problem is a so-called “K”-seal, which is a molded annular lip seal with a free end projecting at an acute angle relative to the piston perimeter. The lip seal is intended to provide a biased, sealing relationship against the inner wall of the cylinder, to reduce blowby. In practice, K-seals have experienced durability issues. Particularly, K-seals are susceptible to tearing with extended use, and also are susceptible to abrasive wear in the event sand or debris becomes trapped in the cylinder, which is not uncommon, due to dirty air lines commonly found on jobsites where compressors are used for driving pneumatic tools.
Thus, there is a need for an improved pneumatic nailer having a more durable piston seal.